Over the years there has been considerable effort to formulate reliable methods and apparatus for measuring the movement of human body parts. Measurements of movement are made to determine if they fall within normal ranges of motion and to provide comparative information for future reference to monitor changes. For many movements, complete definition of a range of motion requires 3-D measurement. Spinal motion is a typical example. The kinematic function of the cervical spine has received considerable attention in recent years because of a large number of people who suffer from back pain.
Abnormal kinematic function of the cervical spine due to cervical sprain or cervical strain injuries resulting from, for example, automobile accidents, which are commonly known as "whiplash injuries," afflict over 1,000,000 Americans annually. Such injuries typically involve soft tissue damage only, and a major medical as well as legal problem is to determine not only the extent of injury at the outset, but also to determine the effects of therapy and medical treatment. Various methods of x-ray analysis (an invasive method) of the head and neck have been proposed. Only skeletal damage and major soft tissue changes can be seen with invasive techniques, and then only in the most severe cases. Computerized Tomography (CT) and Magnetic Resonance Imaging (MRI) studies have similarly been made, but they have failed to provide non-invasive, diagnostic or prognostic parameters to use as a predictor of the clinical condition.
Presently, head range of motion is the accepted non-invasive method for clinical evaluation of neck injuries. This technique, however, does not provide information concerning the exact kinematic function of the cervical spine during head movements. Furthermore, the results of such examinations can easily be swayed by conscious actions of the patient. This invention provides a non-invasive clinical tool for the assessment of neck function that does not suffer from these drawbacks.
The theory of this invention is based on the fact that the head is the final link in an open kinematic chain that includes the neck. Therefore, head movements are the final product of relative rotation about the cervical and upper thoracic vertebral joints with individual contributions depending on active muscle contraction and passive constraints (i.e., ligaments, intervertebral discs and facet orientations). Kinematic redundancy in this system is prevalent. For example, it is possible to produce mid-range, flexion-extension movements by concentrating the vertebral rotation about the upper cervical spine, the lower cervical spine or by distributing the rotation throughout the neck. Because the head is serially linked with the neck, such changes in cervical kinematics will be reflected by corresponding changes in head kinematics. (Chao, E.Y.S., Tanaka S., Korinek and Cahalan, T. (1989) Measurement of neck range and pattern of movement, Abstract 319, XII Int. Congr. Biomech., UCLA, Los. Angeles.). Variations in neck kinematics can be brought forth by injury to soft tissues in certain neck regions (e.g., injury to the upper cervical spine could necessitate rotation about the lower cervical spine). Therefore, head kinematics can provide a "window" to neck function/dysfunction. The kinematics of choice pertain to the head 3-D axis of rotation during specified movements.
The axis of rotation can be described in its finite or instantaneous form. The finite axis of rotation is the directed line in space about which the head rotates during a finite displacement (e.g., head rotation from 0.degree. to 10.degree.). The instantaneous axis is the limiting case of vanishing displacement and, therefore, yields a complete description of cervical function during head movements. Both of these axes can be defined by the screw axis parameters, which include the axis planar crossing (x,y,z coordinates), the axis direction vectors (x,y,z unit vectors), the rotation angle and the sliding component. The axis crossing and direction vector parameters are especially powerful in determining cervical function. For instance, during head extension movements, the crossing vectors correspond to the position of the axis on the mid-sagittal plane, thus giving a measure of cervical level of rotation. The direction vectors then characterize the degree of coupled motion inherent within the movement, thereby providing information concerning asymmetric neck kinematics.
Through experimental testing it has been established that uninjured subjects have constant and similar screw axis patterns during natural head movements and that injured patients tend to alter these patterns in response to their injuries. This allows the present invention to determine the existence and region of neck injury by noting differences in neck kinematic function between patients and normal data bases via the screw axis parameters.
The finite and instantaneous axis of rotation of a rigid body can be found by a variety of mathematical techniques. The finite planar axis can be found by methods such as the classical Rouleaux method (e.g., Panjabi, M. M., "Centers and Angles of Rotation of Body Joints: A Study of Errors and Optimization, " J. Biomechanics, 12:911-920 (1979)) or the rotation matrix method of Spiegelman and Woo, S., "A Rigid-Body Method for Finding Centers of Rotation and Angular Displacements of Planar Joint Motion," J. Biomechanics, 20:715-721 (1985)). These planar aces are a subset of the more general 3-D screw axis analysis but do not provide the 3-D screw axis parameters for the head-neck system.
The 3-D axis for a given finite rotation can be obtained by two mathematically distinct methods, which take advantage of the x,y, and z coordinates of markers attached to the rigid body: i) analysis based on the displacement matrix approach (e.g., Suh, C. H. and Radcliffe, C. W. Kinematics and Mechanisms Design, John Wiley & Sons, N.Y., 1979); and ii) an approach based on minimizing error in the matrix formulation (Spoor, C. W. and Veldpau, F. E. "Rigid body motion calculated from spatial co-ordinates of markers, "J. Biomechanics, 13:391-393 (1980); Woltring, H. J., Huiskes, R., De Lange, A. and Veldpaus, F. E. "Finite centroid and helical axis estimation from noisy landmark measurements in the study of human joint kinematics, " J. Biomechanics, 18:379-389 (1985)). In the first case, the algorithm uses each combination of a 4 markers to estimate the screw axis parameters. Thus, with 5 markers, there are 5 solutions that, in theory, are the same and, with 6 markers, there are 15 such solutions. The best estimate is then either the average or the median of the population. The second method utilizes all markers to estimate the appropriate information, essentially numerically solving an optimization problem. Past results suggest that the latter method is superior. Woltring, H. J., Huiskes, R., De Lange, A. and Veldpaus, F. E. "Finite centroid and helical axis estimation from noisy landmark measurements in this study of human joint kinematic, " J. Biomechanics, 18:379-389 (1985).
This powerful method for determining neck kinematic function via the screw axis parameters of the head, however, has not been used in past investigations. Engineering research on the cervical spine has resulted in a data base in which the basic parameters of cervical range of motion and static relationships of a vertebra to its adjacent vertebrae have been established to a first approximation. A limited amount of data exists in which the planar finite axis (e.g., centrode) has been found for individual vertebral rotations. Clinical Biomechanics of the Spine, White, A. A. and Panjabi, M. M., Second Edition, 1990, J. B. Lippincott, Phila., PA. These two-dimensional methods utilize cadavers or crude invasive techniques (e.g., X-rays) and, furthermore, do not give a measure of overall kinematic cervical function during head movements.
Models of whiplash injury have recently been attempted using both anthropomorphic dummies and computer simulation (reviewed by Winters (1978), Sances et al. (1981)). However, these studies have considered only the general relationship between possible injury modes and crash conditions. Also, the identifying parameters are typically head acceleration and head range of motion in rotation and translation. Screw axis parameters have not been of importance. Few measurements have been made on humans. More importantly, there is little relation between measurement of the kinematics of collision using models and measurement of voluntary movements in humans. None of these "whiplash injury" studies has ever used 3-D kinematic screw axis parameters of the head as a diagnostic tool to determine the extent of abnormal kinematic cervical spine movement. See Winters, J. Biomechanics; Wyss and Pollack, 1981, Med. Biol. Eng. Computers; Panjabi et al., J. Biomech. 14, 1981. Thus, actual non-invasive measurements of the instantaneous or finite axis of rotation have not been used or suggested for use as a predictor or diagnostic parameter of the basic biomechanical lesion produced by the whiplash injury.
U.S. Pat. Nos. 4,664,130 and 4,669,156 to Gracovetsky disclose a non-invasive method and equipment for the detection of a mechanical abnormality or injury in the lumbar or cervical spine of a patient and to identify this abnormality or injury as either of the compression or torsion type. In a first step, any variation of the lumbar curve of the patient is measured using a non-invasive technique. Then any discrepancy or asymmetry is detected in said measured variation of lumbar curve. Gracovetsky does not find the 3-D screw axis parameters of a specific rigid body (e.g., vertebrae or head), and, in fact, cannot obtain the 3-D axis using the method and equipment disclosed therein.
U.S. Pat. No. 4,528,990 to Knowels discloses a head-mounted apparatus for measuring the movement of the spine or head about a substantially vertical axis and is also capable of indicating spine or head tilting. A headband firmly affixed to the head includes an indicia scale used in conjunction with a body reference indicator, whereby the indicator is maintained stationary while the spine or head is rotated such that the relationship between the indicator and indicia scale represents rotative body movement. A gravity-operated gauge is also affixed to the head with respect to the horizontal. This device only measures orientation (angular tilt) and there is no attempt to measure axis of rotation. The same applies to Farrar, U.S. Pat. No. 3,955,562 (1976).
Gilman et al. Instrumentation & Techniques, Measurement of Head Movement During Auditory Localization, Behavior Research Methods & Instrumentation, Vol. II(1), 37-41 (1979), uses a helmet apparatus with one light source marker to determine the angular position and velocity of the head in response to audio signals. The method, however, does not attempt and, in fact, cannot find the 3-D instantaneous or finite head axis of rotation. Even though Gilman et al. discloses that a 3-D system is contemplated, this addition would only allow for the determination of angular position in three axes and would still not provide axis of rotation data.
Gorron et al. discusses the use of x-rays to calculate the instantaneous axis of rotation of the cervical vertebrae, and claims to show that a change from normal occurred in a person's centerline, indicating a dislocation of the C-7 vertebrae. Gorron, J. P., Deschamps, G., Dimnet, J., Fischer, L. P., Kinematic Study of the Inferin Cervical Spine in Saggital Plane, pp. 32-37. In: P. Kehn & W. Widner (eds.) Cervical Spine I Springer-Verlag, N.Y. (1987). This method, however, does not and is not set up to calculate the 3-D screw axis parameters of the head to provide a measure of overall cervical function.
Huntington et al., A Method of Measuring from Photographic Records the Movements of the Knee Joint During Walking, IMechE, Vol. 8, No. 3 (1979), relates to a non-invasive diagnostic method and apparatus for determining real-time patient ranges of motion of the knee joint by utilizing at least one video camera to track and record light reflected from markers attached to the knee joint. Huntington et al. do not disclose the use of screw axis parameters and, furthermore, do not disclose a method or apparatus for use with the head-neck system.
Similar apparatus and methods have been used for study of the jaw, the back and the arm. For example, simple photography has been used to record jaw movement, and plots of the trajectory of jaw movement have been attempted. However, criteria for differentiating normal from abnormal movement have not been used, and the method is not applicable to the head-neck system.
Russian Patent No. 904,666 discloses a device that records an observer's head position while observing an object. A screen is placed on the head of the observer and carries a two point source of light. The measuring element of the point coordinates determines the Cartesian coordinates and transmits two X,Y values to a converter, which describes the movement of the two points and hence the movement of the head. By increasing the number of screens and recorders, the general case with three dimensions can be handled. There is no teaching to obtain screw parameters or to utilize such information as a diagnostic tool.
Berger, U.S. Pat. No. 4,586,515, discloses a device and method for measuring the position and/or motion of a body part, and, particularly, the head to diagnose spinal disorders. Three sensors are used to detect 3-D motion of the head. Rotation, flexion and lateral tilting of the head are detected by the device to determine the motion pattern of the body part in space to diagnose a motion disorder. Berger does not use biochemical screw axis pathways to determine the nature and extent of abnormal head movement.
Thus, despite the various attempts of those skilled in the art, the art has failed to develop a reliable method for determining abnormal kinematic movement of the cervical spine. More particularly, the art has failed to recognize the use of the 3-D kinematic screw axis parameters of the head as an indicator of cervical spine function and, thus, has failed to provide a satisfactory non-invasive method for using the 3-D kinematic screw axis parameters of the head as a diagnostic tool to determine the nature and extent of abnormal kinematic cervical spine movement.
Accordingly, it is a principal object of the present invention to provide a method for using finite and instantaneous 3-D kinematic screw axis parameters as a diagnostic tool to determine the nature and extent of abnormal kinematic cervical spine movement.
It is a more specific object of this invention to provide biomechanical, numerical parameters by which to establish abnormal kinematic function of the cervical spine, which occurs in patients who suffer "whiplash injury."
Yet another object of the invention is to provide a procedure necessary to carry out the above-identified methods.
These and other advantages of the invention as well as additional inventive features will become apparent from the following detailed description of a preferred exemplified embodiment of the invention and accompanying drawings.